Conventionally, iron-based materials have been mainly used for connecting rods, valves, retainers and the like. However, the iron-based materials cannot be positively regarded as the satisfactory materials to meet the demands for lighter engines and higher engine speed because of relatively high specific gravity.
Recently, therefore, titanium alloys with lower specific gravity have started to be used as the materials for the connecting rods of some special automobiles, such as racing cars. Among these titanium alloys, one having a composition given by 6% Al- 4% V-Ti is generally used for the purpose.
In a case of manufacturing the aforesaid component by taking the advantage of a titanium alloy composed of aluminum of 6% and vanadium of 4%, after preparing the above composed titanium alloy, by subjecting an ingot to hot-forging, a product in a desired shape is obtained. And further, if necessary, after subjecting the obtained component to cut machining, it is processed to a finished product.
In general, if the hot forging is conducted at a higher temperature, then the deformability of the ingot material increases, and whereby its forging ability improves in proportion. In the case of the titanium alloy of the aforesaid composition, however, if the hot forging is conducted at a temperature in a .beta. region, which is higher than the temperature in the (.alpha.+.beta.) region, the grain size in the resulting alloy texture is coarse, so that the toughness of the alloy is decreased. It is, therefore, common that the hot-forging is conducted the (.alpha.+.beta.) region. For this reason, the impact value also becomes higher.
When conducting the hot forging in the (.alpha.+.beta.) temperature region, however, it is required to control the entire temperatures of the surface and core portion of the ingot material within the (.alpha.+.beta.) temperature region. The deformability of the titanium alloy of the aforesaid composition in this temperature region is not always high. Therefore, desirable forgability is not attained. In addition, desired machinability is also not attained. In order to industrially supply reliable products in bulk, it is required to maintain high quality of the forgings. However, in the light of the aforesaid reason, in forging, it is required to considerably and strictly control the forging process and further, there are economical problems due to the uncertainty of the workability.
In industrial production, it may be advisable to perform the hot forging in a high-deformability temperature region, e.g., the .beta. region. As mentioned above, however, the hot forging at a temperature in such a .beta. region temperature lowers the toughness of the titanium alloy component, so that it cannot be practically used in view of product quality.
An object of the present invention is to provide a titanium alloy component and a method for manufacturing the same, which is capable of being used in parts of an engine regardless of a slight lowering of toughness in a case of directly hot-forging an ingot of a titanium alloy at an (.alpha.+.beta.) temperature region. A further object of the present invention is to provide a titanium alloy component having a fatigue strength of a equivalent level to a titanium alloy comprising 6% aluminum and 4% vanadium, which is hot forged at an (.alpha.+.beta.) region, and in a case of where maintenance of fatigue strength with stress concentration depending upon a irregular shape is a significant factor.
Another object of the invention is to provide a titanium alloy component and a method for manufacturing the same, which includes higher machinability than a titanium alloy composed of aluminum of 6% and vanadium of 4%. A further object of the present invention is to provide a titanium alloy and a method for manufacturing the same, which are excellent in hot forging ability estimated by ease of forging, controlling temperatures and obtaining high quality forging products.